/*
* Created by boil on 2023/2/17.
*/

#ifndef RENDU_CORE_BASE_ALGORITHM_H_
#define RENDU_CORE_BASE_ALGORITHM_H_

#include <algorithm>
#include <vector>
#include "utility.h"

namespace rendu {
/**
 * @brief Function object to wrap `std::sort` in a class type.
 *
 * Unfortunately, `std::sort` cannot be passed as template argument to a class
 * template or a function template.<br/>
 * This class fills the gap by wrapping some flavors of `std::sort` in a
 * function object.
 */
struct std_sort {
  /**
   * @brief Sorts the elements in a range.
   *
   * Sorts the elements in a range using the given binary comparison function.
   *
   * @tparam It Type of random access iterator.
   * @tparam Compare Type of comparison function object.
   * @tparam Args Types of arguments to forward to the sort function.
   * @param first An iterator to the first element of the range to sort.
   * @param last An iterator past the last element of the range to sort.
   * @param compare A valid comparison function object.
   * @param args Arguments to forward to the sort function, if any.
   */
  template<typename It, typename Compare = std::less<>, typename... Args>
  void operator()(It first, It last, Compare compare = Compare{}, Args &&...args) const {
    std::sort(std::forward<Args>(args)..., std::move(first), std::move(last), std::move(compare));
  }
};

/*! @brief Function object for performing insertion sort. */
struct insertion_sort {
  /**
   * @brief Sorts the elements in a range.
   *
   * Sorts the elements in a range using the given binary comparison function.
   *
   * @tparam It Type of random access iterator.
   * @tparam Compare Type of comparison function object.
   * @param first An iterator to the first element of the range to sort.
   * @param last An iterator past the last element of the range to sort.
   * @param compare A valid comparison function object.
   */
  template<typename It, typename Compare = std::less<>>
  void operator()(It first, It last, Compare compare = Compare{}) const {
    if(first < last) {
      for(auto it = first + 1; it < last; ++it) {
        auto value = std::move(*it);
        auto pre = it;

        for(; pre > first && compare(value, *(pre - 1)); --pre) {
          *pre = std::move(*(pre - 1));
        }

        *pre = std::move(value);
      }
    }
  }
};

/**
 * @brief Function object for performing LSD radix sort.
 * @tparam Bit Number of bits processed per pass.
 * @tparam N Maximum number of bits to sort.
 */
template<std::size_t Bit, std::size_t N>
struct radix_sort {
  static_assert((N % Bit) == 0, "The maximum number of bits to sort must be a multiple of the number of bits processed per pass");

  /**
   * @brief Sorts the elements in a range.
   *
   * Sorts the elements in a range using the given _getter_ to access the
   * actual data to be sorted.
   *
   * This implementation is inspired by the online book
   * [Physically Based Rendering](http://www.pbr-book.org/3ed-2018/Primitives_and_Intersection_Acceleration/Bounding_Volume_Hierarchies.html#RadixSort).
   *
   * @tparam It Type of random access iterator.
   * @tparam Getter Type of _getter_ function object.
   * @param first An iterator to the first element of the range to sort.
   * @param last An iterator past the last element of the range to sort.
   * @param getter A valid _getter_ function object.
   */
  template<typename It, typename Getter = identity>
  void operator()(It first, It last, Getter getter = Getter{}) const {
    if(first < last) {
      constexpr auto passes = N / Bit;

      using value_type = typename std::iterator_traits<It>::value_type;
      std::vector<value_type> aux(std::distance(first, last));

      auto part = [getter = std::move(getter)](auto from, auto to, auto out, auto start) {
        constexpr auto mask = (1 << Bit) - 1;
        constexpr auto buckets = 1 << Bit;

        std::size_t index[buckets]{};
        std::size_t count[buckets]{};

        for(auto it = from; it != to; ++it) {
          ++count[(getter(*it) >> start) & mask];
        }

        for(std::size_t pos{}, end = buckets - 1u; pos < end; ++pos) {
          index[pos + 1u] = index[pos] + count[pos];
        }

        for(auto it = from; it != to; ++it) {
          out[index[(getter(*it) >> start) & mask]++] = std::move(*it);
        }
      };

      for(std::size_t pass = 0; pass < (passes & ~1); pass += 2) {
        part(first, last, aux.begin(), pass * Bit);
        part(aux.begin(), aux.end(), first, (pass + 1) * Bit);
      }

      if constexpr(passes & 1) {
        part(first, last, aux.begin(), (passes - 1) * Bit);
        std::move(aux.begin(), aux.end(), first);
      }
    }
  }
};

} // namespace rendu

#endif //RENDU_CORE_BASE_ALGORITHM_H_
